It is a celebration by the Catholic Church and Eastern Orthodox Churches to celebrate the dead. The Catholic Church celebrates it the day after All Saints Day and the Eastern Orthodox churches...
All Saints Day falls on November 1 and honors all saints, named and unnamed, known and unknown. All Souls Day in on November 2 and on this day we pray for the poor souls waiting in Purgatory. Both...
All Saints' day was instituted to honour all saints, including those who have not been canonized. All Souls' Day was instituted for the souls in purgatory. The Mass on that day is offered for them.